High frequency measuring apparatus



Nav. 22, 1955 w. w. HANSEN er A1. 2,724,800

HIGH FREQUENCY MEASURING APPARATUS t original med sept. 1v, 194s 2sheets-sheet 1 I (LLvyl-/O nvo/cAroR T'HEODORE MORE/V0 YQ/MM w. w.HANSEN E-r AL 2,724,800

HIGH FREQUENCY MEASURING APPARATUS Nov. 22, 1955 Original Filed Sept.17, 1943 2 Sheets-Sheet 2 Nvo/CA To@ METER D/FFRE/WE METER il@ va/0ATaf? /IG'TORNEY United States Patent O HIGH FREQUENCY MEASURINGAPPARATUS William W. Hansen, Stanford University, Calif., and TheodoreMoreno, Cambridge, Mass., assignors to Sperry Rand Corporation, acorporation of Delaware Original application September 17, 1943, SerialNo. 502,734. Divided and this application October 3, 1947, Serial No.777,802

11 Claims. (Cl. 324-95) The present invention pertains to the artincluding devices adapted for use with ultra-high frequency energy and,more particularly, relates to such devices responsive to the directionof energy ow, such as are useful for measuring and/or indicating thepower flow or standing wave ratio in an ultra high frequency energyconductor. The present application is a division of parent applicationSerial No. 502,734, filed September 17, 1943, now issued as Patent No.2,580,678.

In prior copending application Serial No. 499,072, now abandoned, forHigh Frequency Measuring Apparatus, filed August 18, 1943, in the nameof William W. Hansen, there is shown one form of ultra-high-frequencyenergy device using a direction-responsive apparatus and adapted tomeasure separately the power flowing in an ultrahigh-frequency conductorto, or reflected from, a load device. In this prior application is alsoshown apparatus for indicating directly the standing-wave ratio in anultra-high frequency energy conductor. Such measuring devices have thegreat advantage that their indication is independent of their positionalong the energy conductors, and is not affected by standing wavestherein, permitting direct and continuous monitoring, in contrast toprior art devices, whose indications may differ by as much as three-foldaccording to the location of the measuring device along the conductor,because of standing waves.

The present invention comprises improvements in ultra-high-frequencyapparatus of the type disclosed in this prior copending application.More specifically, the present invention contemplates adapting theinvention in the prior application to ultra-high-frequency energyconductors of the wave guide type, and is further directed towardproviding decreased frequency sensitivity for such devices, whileretaining all the advantages thereof.

Accordingly, it is an object of the present invention to provideimproved apparatus responsive to the direction of energy ilow along anultra-high-frequency conductor.

Another object of the present invention is to provide improved apparatusfor measuring or monitoring the ultra high frequency power llow to autilization device or the power reflected from such a device.

It is a further object of the present invention to provide improvedultra high frequency apparatus for measuring or monitoring the powerflow in the wave guide or other high frequency energy conductors,travelling in a predetermined direction.

It is another object of the present invention to provide improvedapparatus for directly indicating and monitoring the standing wave ratioand power transmission eiciency of an ultra high frequency energyconductor.

It is a further object of the present invention to provide improvedapparatus of the above type and of the type disclosed in theabove-mentioned copending application, and having decreased frequencysensitivity.

Other objects and advantages of the present invention will becomeapparent from the following specification and drawings, wherein ICC Fig.1 shows a schematic longitudinal cross-sectional View of one form of thepresent invention.

Fig. 1A shows a longitudinal cross-sectional view of the device of Fig.l taken along line 1A-1A thereof.

Fig. 2 shows a similar schematic longitudinal crosssectional view of amodified form of the present invention.

Fig. 2A shows a cross-sectional View of the device of Fig. 2 taken alongthe line 2A--2A.

Fig. 3 illustrates a similar schematic longitudinal crosssectional viewof another form of the present invention.

Fig. 4 illustrates a longitudinal cross-sectional view of a preferredform of the present invention.

Fig. 5 shows aschematic longitudinal cross-sectional view of a modifiedform of the present invention.

Fig. 5a shows a longitudinal cross-sectional view of the device of Fig.5 taken along the line Sa-Sa thereof.

Referring to Fig. l, there is shown an ultra high frequency energyconductor 11, illustrated as being of the circular wave guide type.Energy is supplied to the wave guide 11 from a suitable source connectedat its left, while a suitable load or utilization device is to beunderstood as being connected to the right end of conductor 11.

For the purpose of measuring the power flow from the source toward theload, and independent of any power reilected by the load, a second orauxiliary wave guide 13 is positioned along and adjacent to wave guide11. Guide 13 preferably has the same propagation constant as guide 11.The guide 13 is terminated at its left end by a suitable terminatingimpedance which may comprise an insulating disc 12 with a resistivecoating 14 producing a desired impedance, so as to prevent rellection ofenergy incident upon this end of the guide 13. At the other end of thisguide 13 is located a suitable detector, or rectifier, indicatedschematically as the crystal detector 16, coupled to guide 13 by loop15.

The guide 13 is excited by a pair of probes or antennae 17, 1S,extending through and suitably insulatingly supported in openings 19, 20in the adjoining walls of wave guides 11 and 13. Preferably probes 17,18 are spaced substantially one-quarter wave-length apart within guide11, at the operating frequency, so as to be eX- cited in substantiallyphase relation.

Energy owing from left to right in guide 11 will excite couplingantennae 17, 18 in 90 phase relation. Antennae 17 and 18 then tend toset up waves travelling in both directions in guide 13. However, theleftward wave in guide 13 excited by antenna 17 is 180 out of phase withrespect to that excited by antenna 18, so that these waves cancel and noresultant leftward wave is produced in guide 13. The rightward wavesexcited by antennae 17 and 18 reinforce, and energy travels down guide13 to loop 15. The right end of guide 13 may be terminated in an energysink or load, or may radiate its energy into space, preferably withoutreection, so that no standing waves are produced therein. Y

Energy flowing from right to left in guide 11 will similarly excite onlya leftward wave in guide 13. This wave is terminated by impedance 12, 14and has no effect on detector 16. Accordingly, guide 13 will beenergized only by high frequency energy moving from left to right in thewave guide 11, and will not respond in any manner to energy travellingin the other direction in wave guide 11.

Detector 16 is connected to a suitable meter or indicator 21, whosedeilection thereby indicates the amplitude of the incident or rightwardowing energy in wave guide 11. If detector 16 is of the square law type,indicator 21 may be calibrated directly in power. If detector 16 is ofthe linear type, indicator 21 may be calibrated directly in voltage orelectric field intensity within 3. the guide iii. For other types ofdetector, indicator 21 may be suitably calibrated to give desiredindications.

if the energy flowing in guide 11i is modulated, indicator 21 neednot-be a d.c. meter, but may be any indicator adapted to indicate theamplitude of the modulated signal, which is a measure of the power orenergy fiow.

It will be understood that a similar type of apparatus may be utilized'to measure the reflected power merely by interchanging the terminatingimpedance 14 and the detector 16. This is also shown in Fig. l, thecorresponding parts being given identical reference characters to thosedescribed above, but ,now` primed.

Also, if desired, both th incident power and the reiiected power may beindicated simultaneously. in such a case a single indicator may replacethe separate indicators, 2l and 21', and if this indicator is of theratio meter type, illustrated at 41 in Fig. 1, adapted to indicate theratio of its input voltages, the ratio of incident to reflected powerinthe system, which is a direct function of the standing wave ratio, canbe indicated directly, thus rendering the system very useful formonitoring purposes. Also, a single indicator 42 adapted to indicate thedifference between the detector outputs may be used, so that the poweractually dissipated in the load may be indicated.

Fig. 2 illustrates a modification of the system of Fig. 1, in which themain energy conductor is shown in the form of a rectangular wave guide11'. An auxiliary rectangular wave guide 13' preferably having the samepropagation constant as guide 11 and extending along the guide 11', isutilized here. Wave guide 13' is suitably terminated at one end, such asthe left end, by a terminating impedance 23 which may be formed as agently tapering wedge of semi-conducting material adapted to dissipatethe energy travelling from right to left in the wave guide 13. If thetermination 23 is made fairly long compared to one wavelength,substantially no reiiection of this leftward travelling energy will beproduced within the wave guide 13.

Wave guide 13' is excited from guide 11 by a pair of openings 2.4, 25spaced one-quarter-wavelength along the guide 11. In this manner, inresponse to energy travelling from left to right within the main guide11', energy will be excited within auxiliary wave guide 13' travellingonly from left to right. Energy travelling from right to left within themain guide 11' will be ineffective to produce any rightward-travellingenergy in the auxiliary wave guide 13', since it will producesubstantial cancellation at opening 2S, and no reections are produced byimpedance 23, similarly to Fig. 1.

This rightwardtravelling energy in auxiliary wave guide 13 is rectifiedby the detector 16 connected to the indicator 21 by a transmission linesection 26, 27. Detector 16 may he located within auxiliary guide i3',as shown schematically in the figure. In this way indicator 21. willagain indicate the rightward energy flow or power in main Wave guide 11.

By interchanging the positions of the terminating irn pedance 23 and thedetector 16, the device may be made responsive solely to the reflectedpower, as in the prior modification. Also, by use of the ratio meter, asdescribed above, the standing Wave ratio or power transmission eiiciencyor ratio of incident to reflected power may be indicated directly ormonitored. By use of a diiference meter, the actualy power delivered tothe load may he indicated.

Figs. and 5a show such a modification which utilizes a pair of couplers,a ratio meter and a diierence meter accordingl to the teaching of themodification of Fig. 1 but which utilizes rectangular wave guidesaccording to the teaching of Fig. 2. It will be recognized that theapparatus of Fig. 5 operates in substantially identical fashion to theapparatus of Fig. 1.

lt will be understood that antennaeV similar to 17, 18 may be used inFig. 2, or the single openings 24, 2S of Fig. 2 may be used in Fig. 1.lf desired, coupling loops similar to 15 may be used in place of eitherholes 24, 25 or antennae 17, 18.

The devices of Figs. 1 and 2 may be sensitive to frequency variations ofthe energy within main guide 11 or 1l'. In order to avoid such frequencysensitivity, a plurality of such couplings extending over a distancelong in comparison with a wavelength may be used in place of the pairedcouplings 17-13 and 1718 of Fig. 1. A plurality of such couplingantennae 23 is shown in Fig. 3.

Ey using a plurality of such couplings suitably spaced apart andextending for a distance of several wavelengths within main guides itland 11', the device is made to improve its directional sensitivity, thatis, to respond only to high frequency energy travelling in apredetermined direction in the main wave guide 11', and is also maderelatively insensitive to changes in the operating frequency. ln thisway, the critical dimensions necessary for the spacing of antennae i7,13 or 17', 18' of Fig. l or openings 24, 2.5 of Fig. 2 are no longerpresent in the device of Fig. 3. ireferably the antennae of Fig. 3, ortheir equivalent couplings, are spaced closer than onehalf wavelengthwithin main guide 11'. Any suitable number may be used, the largernumbers being preferred.

Fig. 4 illustrates a practical embodiment of the present invention inwhich, in place of the plurality of antennas 28, a single elongatedopening 32 between the wave guides B3' and 11 is provided. Opening 32 ispreferably several wavelengths long within guide 11 to provide goodfrequency insensitivity and directional sensitivity and is fairly narrowin width, in order not to unduly distort the electromagnetic iieldswithin the respective wave guides. Slot 32 thus replaces couplings 17,18 of Fig. 1, and another similar slot replaces couplings 17', 18'.

It will be understood that a similar long slot may be used between twoconcentric transmission lines, to indicate energy flow in one of them inthe same manner as in Fig. 4.

Fig. 4 also illustrates a filter for preventing leakage of highfrequency energy from the crystal detector and the connection to theindicator, which may be utilized in any of the preceding modificationsalso. Thus, in Fig. 4 the inner conductor 26 of the coaxial line 26, 27is connected directly to the crystal 16, at one end, and to a low passfilter at the other end. For this purpose the conductor 26 is connectedto an enlarged section 33 which is made substantially one-quarterwavelength long and is succeeded by a relatively small diameter innerconductor section 36 also of one-quarter wavelength. This in turn isfollowed by a quarterwave section 37 of relatively large diameter, allof these sections being insulated from the outer conductor 27. Thissuccession of alternating large and small diameter sections of innerconductor may be extended as far as necessary, and provides a successionof alternately small and large impedance quarter-wave transmission linesections, which, as is well known, serve as an impedance transformer toprovide a greatly decreased impedance to high frequencies at the gapbetween section 33 and conductor 27. Indicator 2l is then connectedbetween the outer conductor 27 and the last inner conductor section 37.Thus the low frequency or direct current energization of indicator 21isunimpeded, while substantially no high frequency leakage occurs.

in this manner we have provided an extremely simple and relativelyfrequency insensitive power measuring and indicating device which isresponsive solely to power flowing in a predetermined direction, andwhich may thereby indicate directly and monitor the power flow orstanding wave ratio in an ultra-high-frequency energy conductor, forexample, a wave guide, without requiring adjustment of any kind.

It willbe understood that Where distances in wavelengths are given, thedistances are measured within the guide, where generallythe wavelengthfor a. given frequency is longer than in free space due to the diiferentvelocities of propagation in the guide and" in free space.

Since many changes could be made in the above construction and manyapparently widely different embodiments of this invention could be madewithout departing from the scope thereof, it is intended that all mattercontained in the above description or shown in the accompanying drawingsshall be interpreted as' illustrative and not in a limiting sense.

What is claimed is:

1. High frequency measuring apparatus for selectively respondingsubstantially exclusively to the power flow in a predetermined directionthrough an ultra-highfrequency wave guide, comprising a second waveguide communicating with said iirst wave guide through a slot that islong compared to the operating wavelength in said rst guide, aterminatingv impedance at one end of said second wave guide, a detectorconnected vat the other end of said wave guide, and means including anoutput circuit connected to said detector for measuring the tlow ofpower in said predetermined direction to the substantial exclusion ofany ow of power in the opposite direction.

2. Apparatus for measuring the tiow of power in a rst wave guide in apredetermined direction substantially exclusively, comprising a secondwave guide, said two guides having cooperating slots extending alongsaid guides for a distance that is long in comparison to a wave lengthof the operating frequency to permit transfer of energy between saidwave guides for ilowing in s'aid predetermined direction in said secondwave guide, means for terminating said second wave guide at one endthereof away from which said energy is flowing, a detector, means forcoupling the detector to the other end of said second wave guide, andindicator means connected to said detector for indicating saiddirectional power flow in said predetermined direction in said firstwave guide to the substantial exclusion of response to any power ow inthe opposite direction.

3. A reiiectometer for measuring standing waves over a wide frequencyrange in a waveguide system including a main waveguide, second and thirdwaveguides aperiodically coupled to said main waveguide over a distanceexceeding a half wavelength at any operating frequency, first wavemagnitude detecting means in said second waveguide responsivesubstantially only to forward-traveling waves in said main waveguide andsecond wave magnitude detecting means in said third waveguide responsivesubstantially only to backwardtraveling waves in said main waveguide.

4. A reilectometer for measuring standing waves in a rectangularwaveguide transmission system connecting a wave generator to a loadincluding a main waveguide having a slot extending for a predetermineddistance longitudinally along each of the wide faces thereof, second andthird waveguides each having one slotted wide face juxtaposed in contactwith said wide faces of said main waveguide and said slots beingjuxtaposed whereby wave energy in said main waveguide is coupled to saidsecond and third waveguides, a first matching resistive load in thegenerator end of said second waveguide, first wave detecting means inthe opposite end of said second waveguide to indicate the magnitudes offorward-traveling waves in said main waveguide, a second matchingresistive load in the load end of said third waveguide, and second wavedetecting means in the opposite end of said third waveguide to indicatethe magnitudes of backward-traveling waves in said main waveguide.

5. A reflectometer for measuring standing waves over a wide frequencyrange in a wave transmission system including a main transmission line,a plurality of means each aperiodically and uniformly coupled to saidmain line over a distance exceeding a half wavelength at any operatingfrequency, first wave magnitude detecting means coupled to one of saidaperiodically coupled means responsivev substantially only toforward-traveling waves on said main line and second wave magnitudedetecting means coupled to another of said aperiodically coupled meansresponsive substantially only to backward-traveling waves on said mainline.

6. A reilectometer for measuring standing waves over a wide frequencyrange in a wave transmission system including a main transmission line,second and third transmission lines aperiodically coupled to said mainline over a distance exceeding a half wavelength at any operatingfrequency, first wave magnitude detecting means coupled to said secondline responsive substantially only to forward-traveling waves on saidmain line and second wave magnitude detecting means coupled to saidthird line responsive substantially only to backward-traveling waves onsaid main line.

7. A directional coupler, including a first length of wave guide whereinoppositely directed energy waves may be propagated, a second length ofwave guide, means interconnecting said first and second lengths of waveguide comprising a common wave guide wall having an aperture therein, athird length of wave guide, means interconnecting said rst and thirdlengths of wave guide comprising a common wave guide wall having anaperture therein, said apertures being spaced along said rst length ofwave guide so as to be non-overlapping, said three lengths of wave guideeach having a rectangular cross-section and operating in a TEM modeduring excitation, said common walls being perpendicular to thedirection of the electric field components existing within the saidthree lengths of wave guide, said second and third lengths of wave guideeach having a wave absorbing section and a wave propagating sectionextending in opposite directions from their respective apertures,whereby a proportion of one of said oppositely directed energy Waves maybe coupled into the wave propagating section of said second length ofwave guide, and whereby a substantially equal proportion of the otherenergy wave may be coupled into the wave propagating section of saidthird length of wave guide.

8. A directional coupler, -including a first length of wave guidewherein oppositely directed energy waves may be propagated, a secondlength of wave guide, means interconnecting said first and secondlengths of Wave guide comprising a common wave guide wall having anaperture therein, a third length of wave guide, means interconnectingsaid irst and third lengths of wave guide comprising a common wave guidewall having an aperture therein, said apertures being spaced along saidrst length of wave guide so as to be non-overlapping, said second andthird lengths of wave guide each having a wave absorbing section and awave propagating section extending in opposite directions from theirrespective apertures, whereby a portion of one of said oppositelydirected energy waves may be coupled into the wave propagating sectionof said second length of wave guide,`

-and whereby a portion of the other energy wave may be coupled into thewave propagating section of said third length of wave guide.

9. A directional coupler, including a rst length of wave guide whereinoppositely directed energy waves may be propagated, a second length ofwave guide, means interconnecting said iirst and second lengths of waveguide comprising a common wave guide wall having an aperture therein, athird length of wave guide, means interconnecting said iirst and thirdlengths of wave guide comprising a common wave guide wall having anaperture therein, said second and third lengths of wave guide eachhaving a wave absorbing section and a wave propagating section extendingin opposite directions from their respective apertures, whereby aportion of one of said oppositely directed energy waves may be coupledinto the wave propagating section of said second length of wave guide,and whereby a portion of the other energy wave may be coupled into thewave propagating section of, saidthird length of wave gui-de.

10. A directional coupler, including a iirst length of wave guidewherein oppositely directed energy waves may be propagated, a secondlength of wave guide, means for directionally coupling said first andsecond lengths of wave guide, a third length of'wave guide, means fordirectionally coupling said rst and third lengths of wave guide, saidsecond and third lengths of wave guide each having a wave absorbingsection and a wave propagating section extending in opposite directionsfrom said directional coupling means, whereby a portion of one of saidoppositely directed energy waves may be coupled into the Wavepropagating section of said second length of wave guide, and whereby aportion of the other energy wave may be coupled into the wavepropagating section of said third length of wave guide.

11. High frequency measuring apparatus for selectively respondingsubstantially exclusively to the power ow in References Cited in the leof this patent UNITED STATES PATENTS 2,151,118 King Mar. 21, 19392,153,728 Southworth Apr. 11, 1939 FOREIGN PATENTS 545,936 Great BritainJune 18, 1942 OTHER REFERENCES Russian publication, Electrosvyaz, vol.IX, No. 4,

20 April 1941, pages 9-15; R. T. P. Translation No. 1525, 9

pages in class 171-95 (23).

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